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pH Control in Flotation of PGM Platinum Group Metal Ores (8 replies and 1 comment)

David Kano
12 months ago
David Kano 12 months ago

Hello, in the flotation of Platinum Group Metal Ores, is it considered wise or cost effective to introduce pH control?  

Is there any mine that mine PGMs that does pH control in their metallurgical plants?

The reason why i ask is because i did some test works. I wanted to check the relationship between grade, recovery, mass pull against pH.(note this was for mainly PGMs) the type ore used has been likened to Merensky with high tulc and alkaline pH. From my observations lab flotation tests I noticed that acidic pulp seemed to float fast, with a high mass pull at first and then the intensity of the froth dies down as time goes by. I was left wondering whether it would be ideal or not to induce acidic conditions so as to lessen residence time in flotation. I am aware of the likely corrosion resulting from acidic conditions.

Victor Bergman
12 months ago
Victor Bergman 12 months ago

There are processes in gold production that are in both basic and acidic and one must know the details so as not misapply any reagents that may cause an upset of the system or process or procedure.

12 months ago
JohnnyD 12 months ago

Most flotation operations are alkaline since this minimizes corrosion and thus initial capital costs and ongoing maintenance.
While it does depend on the nature of the ore of the ore that is being treated, for example, UG2 or Merensky, pH control is rarely applied to these separations. In the case of Platreef ores, there may be a case for some alkaline addition.
At the end of the day, most ores are generally alkaline upon grinding and the recovery of the small quantities of sulfides is also being targeted, particularly nickel.
So an alkaline environment is preferred which occurs naturally without the addition of any alkalies.

Bob Mathias
12 months ago
Bob Mathias 12 months ago

I can't say that I have the specific answers but I can offer some general observations of floating Merensky type ores, which have a moderate and important amount of base metal sulphides present. The dominant sulphide present is usually pyrrhotite followed by pentlandite and chalcopyrite with variable but minor amounts of pyrite, sphalerite, etc., not forgetting the PGM minerals. Some of the PGMS are distributed within the sulphide matrices as well as inclusions and so recovering the sulphides improves PGM recoveries.
I presume that your PGM ore is of similar mineralogical make-up.
Iron sulphides float much better and faster at low pHs (4 to 5) - more oxidizing (collector conversion) and no iron hydroxides to precipitate and limit collection (basis for depression of pyrite at higher pHs with lime which accentuates the effect).
Pentlandite, which is very much like pyrhotite, would be expected to behave similarly.
Chalcopyrite is a hard one to stop from floating at the best of times...so a low pH would not be a barrier for successful recovery.
Native metals and most of the PGM minerals float over a range of pHs, so a lower flotation pH would be acceptable.
Well I guess basically says that a lower pH should be OK for good flotation recoveries with your ore.
Only a few points to note if applying a lower pH:
* low pHs impact collector life (from memory, xanthate has a half-life of 4 hours below pH 5) - you are after dixanthogen (or similar molecule) which is cost-effectively obtained from say PAX

* not sure about some frothers - the lower pH may have an effect on stability; consider less complicated formulations such as MIBC

* corrosion - which you have identified.

You mention that you have an alkaline ore which is common for PGM ores - but how alkaline and does it buffer?
You may need and keep adding lots of acid to get the pH values that you want.
Do you plan to clean the rougher concentrate at an acidic pH or just natural pH after you have re-pulped?

You noted that the intensity of the float 'died' away after the rougher concentrate (majority of floatable minerals) was removed; this would be mainly due to the lack of floating minerals, which 'fortify' the froth structure. With few floatable minerals remaining, the flotation area needs to be decreased significantly (carrying capacity) while adding some more collector (condition) and a strong frother to coax them into the froth.

Another question is what are you doing to control the talc recovery - the approach may be influencing your observations. The 'dying away' of froth after the rougher concentrate had been removed suggests that there is no floatable talc left - either previously recovered or depressed.

Finally, lower residence times are great - less equipment, lower costs - however when you have an existing circuit, there needs to be a significant economic incentive to change anything. So, once you have reliably characterized the improvements (improved PGM recovery would be the main attention grabber), then do a trade-off study : identify all the changes required and associated costs, assume that that the changes can be done where there is a mill re-line or some major maintenance activity (no additional costs due to down time), estimate the operating costs (probably more reagents and maintenance) and compare to the current situation.

John Koenig
12 months ago
John Koenig 12 months ago

Here's a few references to look at:

Muzenda, E., et al., Effect of pH on the Recovery and Grade of Base Metal Sulphides (PGMs) by flotation, 2011.


Valenta, M.M. and Mapheto, H., Application of fundamentals in optimizing platinum concentrator performance, Pt Conf., 2010. http://www.saimm.co.za/Conferences/Pt2010/013-020_Valenta.pdf

Harris et al., A practical approach to plant-scale flotation optimization, JSAIMM, vol. 113(3), 2013, 263-272.


Bill Fraser
12 months ago
Bill Fraser 12 months ago

pH of slurry is generally of alkaline in nature and plays an important part in flotation of minerals. Cu & Pb can be floated around 7-7.5 pH but Zn requires slightly higher pH of 8-9 . Pyrite & Pyrhotite remains in the tails as non-float and can be recovered by cleaning in the acidic pH using Xanthate as the collector.

David Kano
12 months ago
David Kano 12 months ago

In my Lab, to reduce talc recovery- ~500g/t of depressants(finnfix) is used against an average of 80g/t used by SA mines that treat Merensky type of ore( of which Mimosa's ore has been likened to Merensky ore).

More so the collector(SIBX) is used in large quantities, with a dosage rate of ~530g/t, compare to ~60g/t for Merensky

The frother dosage used is much lower compared to typical Merensky operations ~48g/t against ~60g/t.

the recoveries are however lower compared to Merensky operations, they range between 78 and 79% compared to between 85 and 90% for Merensky operations. as such the high talc in the Mimosa ore has and is blamed for high reagent consumption and lower recoveries

Unlike typical Merensky operations, copper sulphate is not added at Mimosa since it is know for activating talc.

however at lower pH, talc is depressed, and possibly reagent consumption would be lowered (i stand to be corrected), and copper sulfate could be possibly added to activate pyrholitite hoping that it wont have a counter effect by activating talc.

David Kano
12 months ago

alkaline condition seem to also favor the flotation of talc, thus diluting the grade and lowering the recoveries

Helena Russell
12 months ago
Helena Russell 12 months ago

When utilizing flotation metods it is very hard to get condistant ph control due to the homogenuality of the ore being trans fered to the mixting tank being homogeneous so at that point ph is shown to be contengent to the ore transferal to the mix tank and the mix of the ore to the extraction solution needs to be constantly monotired at first to assure continuity of the solution utilized to the ore being extracted.

11 months ago
David 11 months ago

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